Problems with snmp collecting data

after i installed and configured my opmanager, i hade added one object to : (linux box) , then it found the linux box and collect some datas, and created ok .

after this , any host added to system or the same first host added don�t have data collected any more .

i made one test : clicked on object , then at resources monitors, then at cpu utilization and click at test monitor , see what it answer :

The Monitor did not respond to the test request !!!

all my objects are with the same problem...

i dont know what is happening , but at the initial discovery it can to read some data from host by snmp no ??? see this :

Linux 2 2.4.21-37.ELsmp #1 SMP Wed Sep 7 13:28:55 EDT 2005 i686 i686 i386 GNU/Linux

i can read host mibs by using "MibBrowser.sh" , but the system no !!! .. whats is happening ???? i tryed 4 times the instalation .

best Regards